Direct drive wind turbines are known in which the gearbox, which is typically arranged between a main shaft and a generator of the wind turbine, is substituted by a multipolar generator. These types of gearless wind turbines do not make use of a gearbox as the wind rotor is connected directly to the rotor of the wind turbine. For this reason, the multipolar generator is also referred to as a directly driven generator. Directly driven generators may be for example synchronous generators with winded rotor or with permanent magnets arranged on the rotor.
One of the main disadvantages of directly driven generators is that their physical dimensions are relatively large. This makes transport and logistics of such generators complex. In addition, the overall weight of such generators involves additional difficulties, for example in assembling, maintenance and/or repair operations.
To at least partially overcome said disadvantages, it is known in the art to make such generators from segments. The use of modular parts for forming, for example, allows manufacturing, transport and handling operations to be reduced.
Examples of such prior art solutions to the above problem are disclosed in EP2063115 and WO2011031165. These documents refer to directly driven generators for a wind turbine in which the stator and the rotor are both formed of segments in order to facilitate transport operations of the generator.
Although modular generators may be advantageous for transport and maintenance or repair operations, the above prior art solutions have the disadvantage that in order to ensure a sufficient stiffness of the generator to withstand operational conditions the generator structure should be oversized. This undesirably leads to higher costs, which in addition does not lead to a better performance.